A. Field of the Invention
This invention relates to an improvement in the melt spinning process for producing undrawn polyhexamethylene adipamide (nylon 66) carpet and tire yarns whereby the spinning productivity in terms of pounds of yarn per unit time is significantly increased.
B. Description of the Prior Art
In the conventional production of melt spun nylon 66 carpet and tire yarns the melt spinning process and drawing process may be carried out in a single operation (i.e. coupled mode) or the processes may be carried out separately (i.e. discontinuous mode). The present invention relates to an improvement in the melt spinning process of the discontinuous mode. In the conventional melt spinning process of the discontinuous mode normally composed of an undrawn yarn from 60 to 420 filaments and having a denier per filament (dpf) between about 30 and about 60 is produced. From the standpoint of economical considerations it is desirable to operate the melt spinning process under conditions which maximize productivity without sacrificing important yarn properties or causing processing difficulties. Conventionally, the yarn is conditioned with steam prior to being wound onto bobbin(s) (i.e. packaged) so as to facilitate packaging. If the yarn is not steam conditioned, the yarn grows (elongates) on and sluffs off the bobbin(s). This is especially a problem in tandem windup process where the filaments (after being quenched) are separated into two bundles or yarns each of which is wound onto its own bobbin. Normally, both yarns have the same number of filaments. In carrying out the process molten nylon 66 is extruded at a given rate through orifices of a spinneret to form a plurality of molten streams. The molten streams cool and elongate as they move away from the spinneret. The cooling is assisted by a stream of flowing air in a quenching chamber, commonly referred to as a chimney. Typically, one side of the filaments is exposed to a stream of transverse air in the chimney. The solidified streams (i.e. filaments) pass over a convergence guide or pair of convergence guides (in the case of the tandem windup process) positioned near the lower end of the chimney. From the chimney the converged filaments, i.e. yarn(s) pass through a conditioning tube into which steam is introduced at a given rate. The convergence guide(s) in the chimney prevent nonuniformity in denier among the filaments which would otherwise result if the filaments were permitted to be whipped about by the steam. Also, in the tandem windup process the convergence guides separate the filaments into two yarns. The yarn(s) are withdrawn from the conditioning tube and forwarded by means of a rotating roll (feed roll) and, optionally, its associated separator roll to a take-up bobbin(s) onto which the yarn is wound to form package(s). The yarn(s) make a sufficient number of wraps (at least a partial wrap) around the feed roll (and separator roll) to prevent the yarn(s) from slipping on the roll. Neither the feed roll nor the separator roll are heated. The feed roll is driven at substantially the same peripheral speed as the take-up bobbin(s) and is correlated with the extrusion rate to provide yarn(s) of a desired dpf. Normally, a spin finish is applied to the yarn(s) between the steam conditioning tube and the feed roll. Normally, the process occupies two floors, one directly over the other. The spinning is carried out on the upper floor and the yarn(s) are packaged on the lower floor. The conditioning tube, sometimes referred to as the "interfloor tube", provides a passage for the yarn(s) between floors. Uncontrolled variations in interfloor pressure and steam conditioning pressure must be avoided in order to obtain a yarn of uniform denier and properties. Proper control of these pressures is troublesome.
The resulting undrawn yarn(s) are then used as feed yarn(s) in a drawing process in which the yarn(s) are drawn to a desired denier. The drawing process may be accomplished in a conventional manner using conventional equipment designed for this purpose and, in the case of carpet yarn, may be coupled with a texturing process. Normally, carpet yarn is drawn at a draw ratio between 2 and 4 and tire yarn is drawn at a draw ratio between 4 and 6.
The productivity of the foregoing melt spinning process is limited in one or more ways. In the case of carpet yarn the process is so-called "quench limited" in that there is a maximum extrusion rate at a constant dpf beyond which the filaments tend to stick to one another at their point of convergence in the chimney. On the other hand, in the case of tire yarn the process is also "property limited" in that there is also a maximum extrusion rate at constant dpf beyond which the elongation of the yarn after being drawn is too low, that is, is unacceptable for tire yarn uses. The extrusion rate at which the process becomes property limited is lower than that at which it becomes quench limited.
Accordingly, it is the main object of the present invention to provide an improvement in the melt spinning process for producing undrawn nylon 66 carpet and tire yarns whereby the productivity of the process in terms of pounds of yarn per unit time is significantly increased.
Other objects and advantages of the invention will become apparent from the detailed description thereof hereinafter.